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Transactions of the Society. 



position, it is advisable to remove the eye-piece and examine the 

 W.A. at the back lens of the objective. The auxiliary lens is sup- 

 plied with a single diaphragm, having a £-in. hole. It is obvious 

 that the use of this diaphragm in no way influences the size of 

 the W.A. 



If the auxiliary lens had increased the resolution by a single 

 jot, it would not have been laid aside, so no one need expect the 

 Thames to be set on fire by its re-introduction. For certain 



objects, such as bacteria and their 

 flagella, it may prove serviceable owing 

 to increase of contrast through the 

 brightening of the field. Mr. Baker 

 has made me a lens from my formula 

 to take the place of the crude plano- 

 convex of former years, and has 

 mounted it in a short tube to hold 

 the single diaphragm. This lens has 

 been tested both by Mr. Merlin and 

 myself, and has been found quite 

 satisfactory. 



Mr. Baker has sent me one of his 

 lamps fitted with my auxiliary lens. 

 Fig. 158 shows the auxiliary lens 

 mounted in a metal screen, and in the 

 position it would occupy when illu- 

 minating an inclined Microscope 

 " direct " without a mirror. The arm 

 which holds the screen consists of two parts, held together by a 

 pinching-screw working in a slot ; this allows the lens not only to 

 be focused, but also to be placed at right angles to the path of an 

 upward, horizontal, or downward beam. This arm is not attached 

 to the pillar itself, but to the sleeve of the arm which holds the 

 lamp-cistern : it can therefore be raised or lowered with the lamp. 

 When its pinching-screw is released, the arm can be moved to one 

 side. It will be noticed that the lens has the diaphragm in position. 

 Some of the Microscope lamps sold by opticians differ in essential 

 particulars from the one I designed thirty years ago, and are quite 

 inefficient. I had nothing whatever to do with the design of several 

 lamps which are named after me. 



Fig. 158. 



